cypher query language

Cypher Query LanguageAndrés Taylor and Alistair Jones

FOSDEM 2012Graph Processing Room5 Feb 2012

Wednesday, February 8, 2012

What is Cypher?

• Graph Query Language for Neo4j

• Aims to make querying simple

Wednesday, February 8, 2012

Motivation

Something new?

• Existing Neo4j query mechanisms were not simple enough

• Too verbose (Java API)

• Too prescriptive (Gremlin)

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Motivation

SQL?

• Unable to express paths

• these are crucial for graph-based reasoning

• neo4j is schema/table free

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Motivation

SPARQL?

• SPARQL designed for a different data model

• namespaces

• properties as nodes

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Design

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Design Decisions

DeclarativeImperative Declarative

follow relationshipbreadth-first vs depth-first

explicit algorithm

specify starting pointspecify desired outcome

algorithm adaptablebased on query

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Design Decisions

Pattern matching

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Design Decisions

Pattern matching

A

B C

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Design Decisions

Pattern matchingA

B C

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Design Decisions

Pattern matchingA

B C

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Design Decisions

Pattern matchingA

B C

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Design Decisions

Pattern matchingA

B C

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Design Decisions

ASCII-art patterns

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Design Decisions

ASCII-art patterns

() --> ()

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Design Decisions

ASCII-art patterns

A B

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Design Decisions

ASCII-art patterns

(A) --> (B)A B

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Design Decisions

ASCII-art patterns

A BLOVES

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Design Decisions

ASCII-art patterns

A -[:LOVES]-> B

A BLOVES

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Design Decisions

ASCII-art patterns

A B C

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Design Decisions

ASCII-art patterns

A --> B --> CA B C

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Design Decisions

ASCII-art patterns

A

B C

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Design Decisions

ASCII-art patterns

A --> B --> C, A --> C

A

B C

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Design Decisions

ASCII-art patterns

A --> B --> C, A --> C

A

B C

A --> B --> C <-- AWednesday, February 8, 2012

Design Decisions

Variable length paths

A B

A B

A B

...

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Design Decisions

Variable length paths

A -[*]-> B

A B

A B

A B

...

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Design Decisions

Optional relationships

A B

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Design Decisions

Optional relationships

A -[?]-> BA B

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Design Decisions

Closures

start london = node(1), moscow = node(2)match path = london -[*]-> moscowwhere all(city in nodes(path) where city.capital = true)

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Design Decisions

Parsed, not an internal DSL

Execution Semantics

Type System

Serialisation

Portability

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Design Decisions

Familiar for SQL users

selectfrom

wheregroup byorder by

startmatchwherereturn

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Implementation

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Implementation

Execution Plan

start n=node(0)return n

Parameters()Nodes(n)Extract([n])ColumnFilter([n])

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Implementation

Execution Plan

start n=node(0)match n-[*]-> b return n.name, n, count(*) order by n.age

Parameters()Nodes(n)PatternMatch(n-[*]->b)Extract([n.name, n])EagerAggregation( keys: [n.name, n], aggregates: [count(*)])Extract([n.age])Sort(n.age ASC)ColumnFilter([n.name,n,count(*)])

Wednesday, February 8, 2012

Implementation

Execution Plan

start n=node(0) match n-[*]-> b return n.name, n, count(*) order by n.name

Parameters()Nodes(n)PatternMatch(n-[*]->b)Extract([n.name, n])Sort(n.name ASC,n ASC)EagerAggregation( keys: [n.name, n], aggregates: [count(*)])ColumnFilter([n.name,n,count(*)])

Wednesday, February 8, 2012

Thanks for Listening!

Questions?Andrés Taylor andres.taylor@neotechnology.com @andres_taylor

Alistair Jones alistair.jones@neotechnology.com @apcj

Wednesday, February 8, 2012